The MAC Scheduler in an eNodeB is responsible for dynamically scheduling the LTE air interface in both the downlink and uplink directions. This scheduling activity needs to accommodate the broad range of air interface features whilst simultaneously optimizing system capacity and delivering Quality of Service (QoS) to users. Within each uplink TTI, the eNodeB must evaluate which UEs require uplink resources, and if possible how much data each UE has/needs to send. Unlike in the downlink, this information is not directly available at the eNodeB. Instead, it is reported by UEs using one of the following:                Scheduling Request (SR) which informs the eNodeB that the UE has an unspecified amount of data to send.        Buffer Status Report (BSR) which informs the eNodeB that the amount of data the UE has to send is within a predefined range. The amount of data available is specified for logical channel groups rather than individual bearers.        
Uplink grant pre-scheduling reserves resources for UE before a scheduling request (SR) is sent, thus it enables uplink packets to be sent faster than if a SR had to be sent.
Uplink prescheduling grants may waste system resources for those cases where the UE has nothing to send and answers a prescheduling grant with an empty BSR and a lot of padding. One example of a solution to solve this problem is to assign absolute low weight for the prescheduling UEs so that, in a higher load situation, the UEs with real traffic and higher weight can obtain the scheduling resources over prescheduling UEs. Thus, the resource wastage can be reduced in some critical situations. However, that also means the prescheduling is only applied in low load situation. In high or medium load situation, it is not possible to guarantee the QoS requirement of the expected QCI, Quality Class Identifier, of the prescheduling UEs. There is a prioritization problem between the prescheduling UEs and the UEs with real traffic or even other prescheduling UEs.